1. Field of the Invention
The present invention relates to a heat sink assembly, and more particularly to a heat sink assembly having a clip assembly which can provide adjustable spring force for positioning a heat sink on an electronic device.
2. Description of Related Art
A heat sink is usually placed in thermal contact with an electronic package such as a central processing unit (CPU), and transfers heat through conduction away from the electronic package so as to prevent over-heating of the electronic package. Usually, a heat sink is secured to an electronic package by using a clip.
Usually, a heat sink clip is for securing a heat sink to a CPU mounted on a CPU socket. Conventionally, the heat sink clip is made from a single piece of metal wire. The heat sink clip comprises a central pressing portion, a pair of resilient portions extending outwardly from opposite sides of the pressing portion respectively, and two arms extending from ends of the resilient portions respectively. A pair of hooks are inwardly formed from ends of the arms respectively. In use, the heat sink is placed on the CPU that is mounted on a printed circuit board. The heat sink clip extends through a channel defined by fins of the heat sink. The pressing portion of the clip rests on a base of the heat sink. The resilient arms are pressed downwardly so that the hooks of the arms are snappingly engaged with undersides of retaining ears of the printed circuit board. Thus the base of the heat sink is resiliently and firmly pressed against the CPU by the pressing portion of the heat sink clip. In this way, the heat sink is securely fastened to the CPU on the printed circuit board by the heat sink clip. US Patent Publication No. 2004/0066626 shows an example of a heat sink clip in a matter mentioned above. However, in operation, the heat sink clip usually fails to produce appropriate spring force acting on the base of the heat sink towards the CPU. The spring force from the heat sink clip is either too weak to firmly secure the heat sink to the CPU, or too strong to possibly damage the CPU. So, a heat sink clip which can provide an adjustable spring force acting on a heat sink towards an electronic device is needed.